The present invention relates to the field of remote plasma sources; more particularly, the present invention relates to transformer coupled plasma sources.
Transformer coupled plasmas are routinely used in a number of different applications including materials processing, production of activated gases, pollutant abatement and many others. In such devices, the magnetic core of the excitation transformer is placed in close proximity to, around or within a vacuum chamber. When the primary winding of this transformer is excited with radio frequency (RF), the electromagnetic fields induced around the core sustain a gas plasma discharge within the vacuum apparatus.
The vacuum chamber is often a metal vessel that includes a dielectric gap to avoid the creation of a closed current loop through the chamber. As the metallic chamber is highly conductive, most of the induced voltage along the chamber drops across this gap. Often, the drop is sufficiently high so as to generate a capacitive discharge across the dielectric gaps.
The capacitive discharge may cause arcs to occur between the plasma and the chamber walls, causing deterioration of the wall coating. In addition, during plasma operation, ions from the plasma may bombard the chamber wall, also resulting in deterioration of the wall because of the sputtering and a chemical reaction between energetic ions and wall material. Therefore, a mechanism to minimize capacitive discharge and ion bombardment of the wall of a plasma chamber is desired.
According to one embodiment, an apparatus is described. The apparatus includes a metal vacuum chamber with two or more dielectric breaks. It also includes a number of excitation transformers located so as to distribute the total induced voltage in the chamber among the dielectric breaks. Distributing the total induced voltage among the breaks results in lower wall damage and, consequently, longer lifetimes for the plasma chambers.